1. Field of the Invention
The present invention relates to a pneumatic constant-velocity running apparatus employing a diaphragm type actuator, in which a portion or the whole of a control circuit for the actuator is formed as a hybrid IC and the hybrid IC portion is fixedly mounted outside of an housing of the actuator so as to improve the control system accuracy and in noise proof property as well as in heat radiating property. Further, the apparatus can be reduced in size.
2. Description of the Prior Art
Heretofore, in a constant-velocity running apparatus employing a diaphragm type actuator of the type as described above, it is general that an actuator and a control circuit are provided separately from each other, and are separately mounted on a vehicle as a driving device and as a controller respectively.
FIG. 1 shows an example of the conventional apparatus. In FIG. 1, a reference numeral 1 designates a diaphragm type actuator; 2 and 3, wires; 4, an accelerator pedal; 5a and 5b throttle links; 6, a throttle valve; 7, an engine; 8, a speed meter; 9, a control unit (control circuit) and 10, an operation panel.
In the foregoing arrangement, the throttle valve 6 is operated by the operation of the accelerator pedal 4 through the wire 3 and the throttle link 5b. The diaphragm type actuator 1 operates the throttle valve 6 through the wire 2 and the throttle link 5a independently of the operation of the accelerator pedal 4. In response to a feed-back signal from the speed meter 8, the control unit 9 applies a command to the diaphragm type actuator 1 so as to set the vehicle velocity at a predetermined constant value.
FIGS. 2A and 2B an arrangement of the diaphragm type actuator 1 shown in FIG. 1. In FIGS. 2A and 2B, a reference numeral 20 designates an actuator housing; 21, a diaphragm attached on the inner circumferential surface of the actuator housing 20; 22, a diaphragm holder supported by the diaphragm 21 and provided at the inside front portion of the actuator housing 20; 23, a spring for urging the diaphragm holder 22 forwards and outwards from the actuator hosing 20; 24, a wire holder provided on the central outside of the diaphragm holder 22; 25, a diaphragm chamber formed in the actuator housing 20; 26, an exhaust solenoid valve for exhausting air in the diaphragm chamber 25 and 27, a negative-pressure port of the exhaust solenoid 26 connected to an engine manifold portion, an external vacuum pump and the like. Further, a reference numeral 28 designates a suction solenoid valve for feeding air into the diaphragm chamber 25; 29, an atmospheric airport of the suction solenoid valve 28 opened in the atmosphere; 30, externally led out wires connected to the exhaust solenoid 26 and the suction solenoid 28; 31, an externally connecting connector connected to the externally led-out wires 30; 32, a housing plate of the housing 20 provided at the rear end portion of the actuator housing 20 and 33, screws for fixing the housing plate 32 to the actuator housing 20.
The operation of the thus arranged actuator will be described hereunder. When constant-velocity running control is set, in response to a deviation of the vehicle velocity, the exhaust solenoid valve 26 is duty-cycle controlled so as to increase the rate of the solenoid ON-time. On the contrary, the suction solenoid valve 26 is duty-cycle controlled in inverse proportion to the deviation of the vehicle velocity so as to reduce the rate of the solenoid velocity ON-time. The foregoing operation has been described as to the case in which an actual vehicle velocity is lower than a set value. On the contrary, the exhaust and suction solenoids 26 and 28 are respectively reversely controlled. When the ON-time of the exhaust solenoid 26 is larger that of the suction solenoid 28, the air pressure is the diaphragm chamber 25 becomes lower than the atmospheric pressure, so that the diaphragm holder 22 is moved in the direction of an arrow A against the force of the spring 23 by the pressure difference between the pressure in the diaphragm chamber 25 and the atmospheric pressure and by the operation of the diaphragm 21. Accordingly, the wire 2 shown in FIG. 1 and held by the wire holder 24 is pulled. If the ON-time of the suction solenoid 28 is longer, the operation is effected reversely.
As a result, the negative pressure in the diaphragm chamber 25 of the actuator 1 is controlled so that the actuator 1 is stroke-controlled such that the duty-cycle control of the exhaust and suction solenoids 26 and 28 are stopped when the deviation of vehicle velocity becomes zero and the stroke in that state is maintained to thereby attain the constant-velocity running state. When a deviation occurs in the vehicle velocity again in the constant-velocity running controlling state, the exhaust and suction solenoid valves 26 and 28 starts to be subjected to duty-cycle control in order to eliminate the deviation in the vehicle velocity.
FIG. 3(A) is a block diagram showing the control circuit 9, etc. of FIG. 2. in FIG. 3(A), a microcomputer 9a, a power source circuit 9b, an input circuit 9c, a reset circuit 9d, an output circuit 9e and a fail-safe circuit 9f for keeping the safety of the output circuit 9e constitute the control circuit 9. A reference numeral 10a designates a main switch for the power source circuit 9b; 10b, a control switch; 10, a cancel switch for cancelling a constant-velocity setting and 34, a speed sensor for detecting the vehicle velocity. An output terminal of the output circuit 9e is connected to input terminals of the exhaust and suction solenoid valve 26 and 28 and a coil of, for example, a external vacuum pump (not shown) connected to the exhaust solenoid valve 26 [see the reference numeral 27a in FIG. 3(B)].
FIG. 3(B) is a further detailed circuit diagram showing the output circuit 9e, the fail-safe circuit 9f, and so on. In FIG. 3(B), a reference numeral 35 designates a first transistor having an emitter grounded and a reference numeral 36 designates a second transistor having an emitter connected to a power source so that the level of the output of the transistor 36 is made "H" or "L" in response to the on or off state of the first transistor 35. Reference numerals 37a, 37b, and 37c designate NOR gates, and 38a, 38b, and 38c designate pull-up resistors for pulling up respective connection lines which connect one-line terminals of the respective NOR gates 37a through 37c to the microcomputer 9a. The other input terminals of the respective NOR gates 37a through 37c are commonly connected to the output side of, that is, the collector of the transistor 36. Reference numerals 39a, 39b, and 39c designate current limiting resistors which connect the respective output terminals of the NOR gates 37a through 37c to the respective bases of emittergrounded transistors 40a, 40b and 40c, respectively. The respective collectors of the transistors 40a, 40b and 40c are commonly connected to a power source Vcc respectively through a coil 27a of the external vacuum pump, a coil 26a of the exhaust solenoid valve 26, and a coil 28a of the suction solenoid valve 28. A reference symbols R.sub.1 through R.sub.3 designate resistors, and ZD.sub.1 and ZD.sub.3 designate Zener diodes, respectively.
The operation of the output circuit 9, the fail-safe circuit 9f, and so on will be described hereunder. When the first transistor 35 is in the off-state, the second transistor 36 is also in the off-state, so that the one input of each of the NOR gates 37a through 37c is in the "L" level. Accordingly, the outputs of the NOR gates 37a through 37c depend on a control output of the microcomputer 9a. Each of the three transistors 40a through 40e is turned on or off in accordance with the "L" or "H" level of the microcomputer 9a respectively, and the coils 27a, 26a, and 28a are turned on/off in accordance with the on/off state of the transistors 40a through 40c respectively.
Upon generation of abnormality, when the first transistor 35 is turned on, the second transistor is also turned on, so that a signal in the "H" level is applied to the one input terminal of each of the NOR gates 37a through 37c. Accordingly, the respective outputs of the NOR gates 37a through 37c are always in the "L" level, the transistors 40a through 40c are always in the off-state, and the coils 26a, 27a, and 28a are in the off-state. That is, fail-safe is attained.
Being arranged in such a manner as described above, the conventional pneumatic constant-velocity running apparatus has problems as follows. The drive control portion of the exhaust and the suction solenoid valves 26 and 28 is incorporated in the separately provided control unit 9. Accordingly, the diaphragm actuator 1 is connected to the control unit 9 through the connector 31, the externally led-out wires 30, and a intermediate harness, and the distance between the diaphragm actuator 1 and the control unit 9 differs with the kind of car. If the length of the harness becomes longer, the resistance and the inductance of the exhaust and suction solenoid valves 26 and 28 increase to make the sucking force property as well as the response property of the exhaust and suction solenoid valves 26 and 28 change. Further, since the lengths of the harnesses differ with cars, even diaphragm type actuators having the same performance may vary in properties with cars on which the pneumatic driving apparatuses are mounted. Further, if the length of the harness becomes so long, not only the noise-proof property becomes poor but the connectors for connecting the diaphragm type actuator 1 and the control unit 9 with each other are increased in number so that the probability of faulty connection increases to deteriorate the reliability. Furthermore, the control unit 9 is provided separately from the actuator 1 so that the occupying area therefor increases inconventionally in view of reduction in size of the apparatus. Further, since the driving portion of the control unit 9 for drive-controlling the actuator generates heat, it is necessary to provide means such as a heat sink for radiating the heat resulting in making the control device 9 larger and cause a problem of limitation in mounting area of the control unit 9. Furthermore, generally, the control accuracy of the control unit 9 is determined on the basis of the total variations in the various elements of the control unit 9 so as to grasp the respective gains of the car and the actuator 1 as representative values, and the thus obtained representative values are adjusted to an average gain value which relatively matches the representative values to thereby complete the adjustment. As a result, it could not be avoided that there happens a combination of an actuator 1 and a car which is inconvenient in function due to variations in actuators as well as in cars, resulting in poor reputation as a claim in market.